A vertical take-off and landing (VTOL) aircraft is one that can take off, hover, and land vertically. This classification of aircraft can include a variety of types of aircraft, including tiltrotor aircraft. Tiltrotor aircraft are aircraft that generate lift and propulsion by way of one or more powered rotors (sometimes referred to as “proprotors”) mounted on rotating engine pods, or “nacelles,” usually located at the ends of a fixed wing or an engine mounted in the fuselage with drive shafts transferring power to rotor assemblies mounted on the wingtips. Tiltrotor aircraft combine the vertical lift capability of a helicopter with the speed and range of a conventional fixed-wing aircraft. For vertical flight, the rotors are angled so the plane of rotation is horizontal, lifting the way a helicopter rotor does. As the aircraft gains speed, the rotors are progressively tilted forward, with the plane of rotation eventually becoming vertical. In this mode, the wing provides the lift and the rotor provides thrust as a propeller. Since the rotors can be configured to be more efficient for propulsion (e.g. with root-tip twist) and it avoids a helicopter's issues of retreating blade stall, tiltrotor aircraft can achieve higher speeds than helicopters.